Undrained friction angle

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undrained friction angle

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Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. I am working on a project where I need to determine the phi angle of an overconsolidated clay for retaining wall design.

I have been informed by colleagues that the best way is to infer this data is from correlations with PI and that triaxial testing on clays typically yields phi angles of around 0 representing short term conditions. Is this correct and if so is there a more direct way to determine a long-term phi angle in a clay? I've been told a few times that 10 degrees is a conservative number for clays.

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But I'm not a geotech. Thanks Jayrod I too have been directed towards that sort of value with advice to keep it conservative. Undrained friction angles in clays are often taken as 0 degrees.Lecture No.

October 22, As a result, most of the ex ternal loading is taken by the pore water, resulting in an increase in the pore water pressure.

On the Use of Soil Drained and Undrained Parameters

If the rate of loading is fast enough e. Undrained Undrained Condition Condition. Undrained Undrained or or Drained?

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Loading Loading Frame Frame. Proving Proving Ring Ring. Triaxial Triaxial Cell Cell. Failure was observed when the stress exerted by the plunger was kPa and the pore water pressure recorded was 54 kPa. Learn more about Scribd Membership Home.

Read Free For 30 Days. Much more than documents. Discover everything Scribd has to offer, including books and audiobooks from major publishers. Start Free Trial Cancel anytime. Undrained and Drained Shear Strength. Uploaded by etecham. Document Information click to expand document information Date uploaded Jan 10, Did you find this document useful?

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Search inside document. DrainedDrained ConditionCondition. HigherHigher effectiveeffective. LowerLower effectiveeffective. II LL.Zhongkun Ouyang, Paul W. Copyright remains with the author s or their institution s. Permission for reuse free in most cases can be obtained from RightsLink. An existing effective stress limit plasticity solution for piezocone penetration tests CPTu is calibrated to evaluate the effective stress friction angle for undrained conditions for a variety of fine-grained soils ranging from natural lean to plastic clays and clayey silts from marine, alluvial, lacustrine, deltaic, and glaciofluvial origins.

Data from clay sites are compiled to examine the CPTu-interpreted values in comparison with laboratory benchmark values obtained from undrained consolidated anisotropic CAUC and undrained compression CIUC triaxial tests made on undisturbed samples.

An approximate inversion of the theoretical solution is developed to allow profiles of to be evaluated with depth. Five well-documented case studies in Illinois, Louisiana, South Carolina, Ireland, and Massachusetts are presented to illustrate the application of the solution.

Lastly, results from 1 g chamber tests involving kaolin and kaolinitic—silica mixtures tested by miniature piezocone probes are shown for additional verification. Keywords: claylimit plasticity solutioncone penetrometerfriction anglepiezoconestrength. The piezocone penetration test CPTu is a quick in situ test that permits the delineation of soil stratigraphy and the interpretation of geoparameters with depth in an efficient, economic, and expedient manner.

Details concerning the CPTu equipment, field test procedures, and interpretations are given by Lunne et al. The piezocone penetration test provides three separate readings with depth, including uncorrected cone tip resistance q csleeve friction f sand pore-water pressure at the shoulder u 2.

For the CPTu, an effective stress limit plasticity solution has been developed for the evaluation of the effective stress friction angle for drained to undrained penetration for a variety of soils ranging from sands to silts to clays, as documented by the Norwegian Institute of Technology NTH and detailed by Janbu and SennesetSenneset and JanbuSenneset et al.

While the NTH solution has been used in Norway and parts of Sweden for some time, little appreciation and application has been acknowledged in other countries. Thus, the intent of this paper is four-fold: i review the procedures for assessingii introduce an approximate version of this solution, iii present several case study examples, and iv provide a collection of data from a number of worldwide sites to compare reference values from laboratory triaxial tests with values of interpreted from corresponding CPTu soundings.

All triaxial tests were of the compression type mode under undrained loading i. Generally, the value of was defined at maximum deviatoric stress; however, in some cases an alternative definition e. Also, in several circumstances, was reported by the source, but the actual criterion used was not documented. Additional discussion on the choice of this criterion is given in a later section of this paper.

Janbu and Senneset proposed an effective stress limit plasticity solution for the CPTu towards the evaluation of for undrained penetration. In this approach, the cone resistance number N m is defined as 1.

The tip bearing capacity factor, N qand the pore-water pressure bearing factor, N uare given by Senneset et al. The full solution allows for an interpretation of a paired set of effective stress Mohr—Coulomb strength parameters effective cohesion intercept,and for all soil types, including: sands, silts, and clays, as well as mixed soils Sandven ; Mayne The parameter N q is the tip bearing capacity factor from limit plasticity solutions that is well known for pile foundations.

The parameter N u is a pore-water pressure bearing factor Senneset et al. The NTH analytical model was calibrated by Sandven using data from six onshore and one offshore clays from Norway, as well as supported by finite element simulations. Thus, a relationship between and the cone parameters Q and B q can be expressed as a single equation 5.

A full inversion of eq. The approximate solution is also presented in Fig. In early presentations of the NTH solution e. However, both studies were based on limited data, mainly from the North Sea and Norway, the latter also known for having sensitive to quick deposits.

A special database was compiled from natural deposits of clay, silty clay, and clayey silt that were subjected to both field CPTu and laboratory triaxial compression tests, as documented in Table 1. Geologic origins of these soils include marine, alluvial, estuarine, glacial, deltaic, and lacustrine.

The specific names of these sites, their locations, and their corresponding reference sources that reported the piezocone and triaxial data are noted in Table 1. The CPTu input parameters Q and B q needed for the NTH analysis and the mean values of laboratory-measured water content, plasticity, and benchmark results are also given.

The mean value of PI was Log In. Thank you for helping keep Eng-Tips Forums free from inappropriate posts. The Eng-Tips staff will check this out and take appropriate action. Click Here to join Eng-Tips and talk with other members! Already a Member? Join your peers on the Internet's largest technical engineering professional community. It's easy to join and it's free.

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undrained friction angle

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Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. Beeing in the offshore industry we follow API as recommendation for driven pile capacity. Cohesive material are treated as undrained and we normally perform UUs at different depths in a layer. I have never heard of this is bog standrad soil mechanics. I am interested now Are you perchance looking at a phi-cu analysis?

It gives you Su as a fn of Sigma'fc consolidation stress on the failure plane? That's one of the best general references on undrained strength that there is.

Phi is never really zero anyway; that's just a convenient fiction sometimes. If the clay in situ is not fully saturated, you may still have poor drainage, but the application of stress doesn't result in the same increase in pore pressure and you will get some undrained friction angle.Loads from foundations and walls apply stresses in the ground. Settlements are caused by strains in the ground. To analyse the conditions within a material under loading, we must consider the stress-strain behaviour.

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The relationship between a strain and stress is termed stiffness. The maximum value of stress that may be sustained is termed strength. Stresses and strains occur in all directions and to do settlement and stability analyses it is often necessary to relate the stresses in a particular direction to those in other directions.

Note that compressive stresses and strains are positive, counter-clockwise shear stress and strain are positive, and that these are total stresses see effective stress. Special stress and strain states Analysis of stress and strain In general, the stresses and strains in the three dimensions will all be different.

There are three special cases which are important in ground engineering:. Relevant to conditions below wide foundations or relatively thin compressible soil layers.

In general, the stresses on another plane will be different. To visualise the stresses on all the possible planes, a graph called the Mohr circle is drawn by plotting a normal stress, shear stress point for a plane at every possible angle. In the Mohr circle construction t' is the radius of the circle and s' defines its centre. The shear strength of a material is most simply described as the maximum shear stress it can sustain: When the shear stress t is increased, the shear strain g increases; there will be a limiting condition at which the shear strain becomes very large and the material fails; the shear stress t f is then the shear strength of the material.

The simple type of failure shown here is associated with ductile or plastic materials. If the material is brittle like a piece of chalkthe failure may be sudden and catastrophic with loss of strength after failure. In each case, however, failure is associated with the limiting radius of the Mohr circle, i. The following common examples are shown in terms of total stresses:.

Hence vertical and horizontal stresses are equal and the Mohr circle becomes a point. A strength criterion is a formula which relates the strength of a material to some other parameters: these are material parameters and may include other stresses.

undrained friction angle

For soils there are three important strength criteria: the correct criterion depends on the nature of the soil and on whether the loading is drained or undrained. In General, course grained soils will "drain" very quickly in engineering terms following loading. Thefore development of excess pore pressure will not occur; volume change associated with increments of effective stress will control the behaviour and the Mohr-Coulomb criteria will be valid.

Fine grained saturated soils will respond to loading initially by generating excess pore water pressures and remaining at constant volume. At this stage the Tresca criteria, which uses total stress to represent undrained behaviour, should be used.

This is the short term or immediate loading response. Once the pore pressure has dissapated, after a certain time, the effective stresses have incresed and the Mohr-Coulomb criterion will describe the strength mobilised. This is the long term loading response. The shear strength t f is a material parameter which is known as the undrained shear strength s u. The strength increases linearly with increasing normal stress and is zero when the normal stress is zero. In soils, the Mohr-Coulomb criterion applies when the normal stress is an effective normal stress.

In soils, the cohesion in the effective stress Mohr-Coulomb criterion is not the same as the cohesion or undrained strength s u in the Tresca criterion.

Often this is due to fitting a c', f ' line to the experimental data and an 'apparent' cohesion may be deduced due to suction or dilatancy.Porous materials like soils have different design properties under drained and undrained conditions. This is because of the large permeability of the material so that the pore water can quickly drain out.

On the other hand, due to the low material permeability, undrained condition almost always exist for clays and silts when subjected to quick static loads and earthquake loads. In this article we want to clarify what type of parameters drained or undrained should be used in the typical geotechnical analyses listed below:.

In case of liquefaction where unloading condition exists, the common approach is to either use residual strength parameters of liquefied soil per Idriss and Boulanger guidelines or adopt advanced constitutive models for which the input parameters are drained parameters.

Figure 1. Comparing drained and undrained strength of saturated clays. Undrained shear strength is not a fundamental soil parameter. It generally varies over depth as a function of insitu confining stress at a given depth. Note that larger confining stress reduces void ratio over the historical time.

By the decrease of void ratio, undrained shear strength increases. For overconsolidated clays, c' is not very large and is typically within the range of 0 to psf. By dissipation of pore water pressure, i. Figure 2 presents one of the well-established correlations.

Figure 2. If the groundwater level is way too deep from the ground surface metresfor clay soils, can undrained parametres be used? I believe it would be too conservative to use undrained parameters. I would use drained parameters. Depends on the type of staged construction that you are referring to, but my first intuition would be to use UU parameters since it is generally more conservative.

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Skip to content. Leave a Reply Cancel reply Your email address will not be published.Shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that a soil can sustain. The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts.

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Due to interlocking, particulate material may expand or contract in volume as it is subject to shear strains. If soil expands its volume, the density of particles will decrease and the strength will decrease; in this case, the peak strength would be followed by a reduction of shear stress. The stress-strain relationship levels off when the material stops expanding or contracting, and when interparticle bonds are broken.

The theoretical state at which the shear stress and density remain constant while the shear strain increases may be called the critical state, steady state, or residual strength.

Shear strength (soil)

The volume change behavior and interparticle friction depend on the density of the particles, the intergranular contact forces, and to a somewhat lesser extent, other factors such as the rate of shearing and the direction of the shear stress. The average normal intergranular contact force per unit area is called the effective stress. If water is not allowed to flow in or out of the soil, the stress path is called an undrained stress path. During undrained shear, if the particles are surrounded by a nearly incompressible fluid such as water, then the density of the particles cannot change without drainage, but the water pressure and effective stress will change.

On the other hand, if the fluids are allowed to freely drain out of the pores, then the pore pressures will remain constant and the test path is called a drained stress path. The soil is free to dilate or contract during shear if the soil is drained.

In reality, soil is partially drained, somewhere between the perfectly undrained and drained idealized conditions. The shear strength of soil depends on the effective stress, the drainage conditions, the density of the particles, the rate of strain, and the direction of the strain.

For undrained, constant volume shearing, the Tresca theory may be used to predict the shear strength, but for drained conditions, the Mohr—Coulomb theory may be used. Two important theories of soil shear are the critical state theory and the steady state theory. There are key differences between the critical state condition and the steady state condition and the resulting theory corresponding to each of these conditions.

The stress-strain relationship of soils, and therefore the shearing strength, is affected Poulos by:.

undrained friction angle

This term describes a type of shear strength in soil mechanics as distinct from drained strength. Conceptually, there is no such thing as the undrained strength of a soil.

It depends on a number of factors, the main ones being:. Undrained strength is typically defined by Tresca theorybased on Mohr's circle as:.


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